Colored organic derivatives of cellulose and method of making same



Patented Aug. 30, 1938 UNITED STATES FATE OFFIQE William Whitehead, Cumberland, Md, assignmto Celanese Corporation of America, a corporation of Delaware No Drawing. Application July 25, 1934, SerialNo. 736,909

4 Claims.

This invention relates to artificial materials, such as yarns, filaments and toils containing an organic derivative of cellulose having color imparted thereto by incorporating in the artificial 5 material a vat dye material such as indigoid which has been reduced to a finely divided state and otherwise made ready for a quick and easy dispersion in the dope or spinning solution from which the articles are formed.

An object of the invention is the incorporation, in an economical and expeditious manner, of a vat dye in an artificial film or filament. Other objects of the invention will appear from the following detailed description.

In including pigments and coloring matter in artificial material it is desirable in some cases to have the particle size of the included material as small .as possible. This is especially true when forming filaments which are of such a fine diam- 20 eter that they would be greatly weakened by relatively large crystals or particles of included material which tends to break the continuity of the mass material of the filament.

By employing this invention a deep color may be imparted to artificial material such as filaments and foils, that is fast to light and acid and that may be topped to any desired shade. The coloring material is evenly and thoroughly dispersed and is in such a fine state of subdivision as to not materially interfere with the strength of the material or cause a fluorescence.

According to my invention I reduce or otherwise treat vat dyestufis to form leuco or other compounds of the vat dyestuffs, as indigo-type dye materials, which compounds are soluble in acetone or other solvents for organic derivative of cellulose and which may be added to a solution containing organic derivatives of cellulose, from which filaments, foils and yarns or other artificial products are formed, thus effecting an even dispersion of the dye material in the resulting product. The leuco dye compound may be converted to the insoluble colored state before or upon incorporation with the main bulk of the dope or spinning solution of organic derivative of cellulose or after the products are shaped therefrom and the solvent removed.

The artificial material to be colored by this invention may be yarns, filaments, straws, films, foils or moulded articles made of or containing reconstituted cellulose, regenerated cellulose or cellulose derivatives. The cellulose derivatives that lend themselves to this invention are'cellulose nitrate and the organic esters of cellulose and the cellulose ethers. Examples of organic esters of cellulose are cellulose acetate, cellulose formate, cellulose propionate and cellulose butyrate while examples of cellulose ethers are methyl cellulose, ethyl cellulose and benzyl cellulose.

These cellulosic materials may be formed into filaments, yarns and foils by any suitable method. For example, the organic derivatives of cellulose may be dissolved in a solvent of low boiling point and extruded through predetermined sized orifices into a precipitating bath or into an evaporative medium to separate the solid material from the solvent. Further the solutions may be extruded or cast upon a film forming wheel by methods known in the art. To these solutions, known as dopes or spinning solutions, there is to be dispersed coloring material in such a state of subdivision that they will not merely pass through the spinning orifices but so that they will not materially weaken the final product. In wet spinning or casting processes, as an insurance that all the coloring material is oxidized, there may be added, a small amount of an oxidizing compound to the precipitating bath.

Heretofore it has been very expensive to mill vat dyestufis especially indigo-type pigments fine enough for the incorporation thereof in a spinning solution. Long milling periods were required lasting for days, which long periods often caused recrystallization or regrouping of the dyestuffparticles as the same was being broken down or milled. The milling operation, although not producing the best results,'was very expensive in the amount of time and machinery employed. By this invention the vat dyestuifs, for example of the indigo-type, are rendered in very fine form and are more readily dispersed in the spinning solution due to the method of preparation.

Any of the vat dyestuffs maybe employed which are insoluble or relatively insoluble in the solvent employed in the spinning solution, but the leuco compounds of which are soluble in the solvent of the spinning solution or in a solvent compatible with the spinning solution. For example the anthraquinone vat dyestuffs may be employed or more especially the indigoid vat dyestuffs. As an example and not as a. limitation, natural or synthetic indigo or the various derivatives of same may be employed.

The leuco compounds of these vat dyestufis may be formed by reducing the dyestuff in any suitable manner. Thus the dyestuffs may be reduced by electrolytic reduction, e. g. powdered dyestuffs are suspended in water with or without 1 to 5% addition of sodium hydroxide or its equivalent under a layer of oil and a lead cathode employed with current densities of 1 to 400 milliamperes. In place of or as an aid tothe sodium hydroxide, there may be employed any alkaline hydroxide ammonia or triethanolamines. Other metals besides lead may be used as the cathode. A preferred method, however, is to form the leuco compounds by agitating the vat dyestuif in a solvent for its leuco compound together with finely divided metallic galvanic couples such as zinc and copper dust, then filtering off the dust and any unreduced vat dyestuff. Other metal couples may be employed, for example, aluminum and copper. The leuco compound of the vat dyestuff may also be produced by agitating the dyestuff with sodium hydrosulphite and similar materials. It is advisable to employ insufficient hydrosulphite to completely reduce the dyestuff and then filter off any unreduced dyestuff'thus avoiding any free hydrosulphite in the spinning dope or solution that might cause corrosion of metal parts or attack on the derivatives of cellulose. The leuco compound of a vat dyestuff prepared by either of the above mentioned methods or by other suitable methods may then be mixed with a solution of an organic derivative in a suitable solvent while at the same time allowing the leuco compound to oxidize. As an example a solution containing from to 70%, preferably to by weight of cellulose acetate dissolved in acetone may be placed in a bladed mixer and any desired quantity of the leuco compound added and the same mixed for about 24 hours. During this time the leuco compound is oxidized back to the vat dyestuff and is kept from forming large crystals or grouping into large lumps. The mixing and oxidizing time may be greatly reduced sometimes by as much as 50% or more by adding to the mixture while kneading a small quantity, say 0.08 to 0.3%, of hydrogen peroxide or other oxidizing agent.

The solution or paste, as the case may be, taken from the kneader and containing the finely divided vat dyestuff may be added to a spinning solution of the same or another organic derivative of cellulose dissolved in the same or any other solvent compatible with the solvent employed in the kneading and oxidizing step. The spinning solution maythen be extruded through orifices to form filaments and yarns, cast upon a wheel to form foils or otherwise processed into finished products.

Any suitable solvents may be employed in the oxidizing and kneading operation and as the solvent of the spinning solution. Examples of solvents for organic derivatives of cellulose are acetone, mixtures of acetone and water, mixtures of acetone and methyl or ethyl alcohol, chloroform, ethylene dichloride, mixtures of ethylene dichloride and ethyl or methyl alcohol and mixtures of methyl chloride and ethyl or methyl alcohol.

As illustration and not as limitations the following example is given, it being understood that equivalent chemicals and various percents of reagents may be employed.

Example A charge consisting of 20 parts by weight of zinc dust, 20 parts of copper dust, 400 parts acetone and 100 parts of indigotin (synthetic), Color Index No. 1177, is shaken for 24 hours giving a yield of about 45% leuco compound of indigotin. An equilibrium appears to be reached after conversion of about 45% but after removal of the acetone solution of the leuco compound and addition of fresh acetone for three or four treatments an almost complete reduction of the indigotin is accomplished. 5

About 0.5 to 2 parts by weight of leuco com pound is placed in a kneader containing 100 parts of cellulose acetate and a mixture of acetone and water added to form a 60% solution of the cellulose acetate. About 01% hydrogen peroxide is 10 added and the mixture kneaded for about 12 hours. The soluble leuco compound is oxidized and is present in the solution in the form of extremelyfine particles, which are milled into the cellulose acetate paste or viscous solution and 15 prevented from grouping into larger groups or crystals. Over of the reconverted indigotin is less than one half of a micron in size.

A spinning solution may be formed of 1 part cellulose acetate, 3 parts acetone water solvent .50 and a desired amount of paste containing the reconverted, finely divided indigotin and the same extruded through suitable orifices to form filaments and yarns. The yarns in this particular case are colored a deep blue that is fast to light and acid fading. Obviously if other vat dyestuffs are employed as the starting material other colors will be produced in the yarns.

As an alternative, organic derivative of cellulose chips may be formed by carefully adding 441!) the leuco compound to a plastic mass formed of an organicderivative of cellulose and a volatile solvent while kneading same, the oxidation of the leuco compound taking place during kneading. The mass so formed may then be worked between 513.; heated malaxating rolls to form sheets or slabs which may then be broken into chips. These chips, which contain the vat dyestuff in very finely divided form, may then be added to the dope or spinning solution in such amounts as 110. 40 yield the desired concentration of vat dyestuff.

It is to be understood that the foregoing detailed description is merely given by way of illustration and many alterations may be made therein without departing from the spirit of my invention.

Having described my invention what I desire to secure by'Letters Patent is:

1. Process for the production of solutions for use in the manufacture of colored artificial filawim ments and similar articles, which comprises agitating inacetone a .powdered metallic galvanic couple and an indigo-type vat dyestuff which is insoluble .in acetone but the leuco compound of which is soluble in acetone, removing said gal-m3 vanic couple and excess unchanged vat dyestuif from the resulting solution of the leuco compound, kneading the acetone solution obtained with a plastic mass having a basis of a substance selected from the group consisting of cellulose formate co.

cellulose acetate, cellulose propionate, cellulose butyrate, -methyl cellulose, ethyl cellulose and benzyl cellulose and containing a small percentage of hydrogen peroxide and adding the resulting product to a solution of said substance. as; 2. Process for the production of solutions for use in the manufacture of colored artificial filaments and similar articles having a basis of cellulose acetate, which comprises agitating in acetone a powdered metallic galvanic couple and r an indigo-type vat dyestufi which is insoluble in acetone but the leuco compound of which is soluble in acetone, removing said galvanic couple and excess unchanged vat dyestuff from the resulting solution of the leuco compound, kneading the acetone solution obtained with a plastic mass having a basis of cellulose acetate and containing a small percentage of hydrogen peroxide and adding the resulting product to a solution of cellulose acetate.

3. Process for the production of solutions for use in the manufacture of colored artificial filaments and similar articles, Which comprises reducing an acetone-insoluble indigo-type vat dyestuff, yielding an acetone-soluble leuco compound, in the presence of acetone so as to obtain a solution of the free leuco compound, removing insoluble material from such solution, oxidizing the leuco compound by kneading such acetone solution under oxidizing conditions With a plastic mass having a basis of cellulose acetate and then incorporating the kneaded mass in an acetone solution of cellulose acetate.

4. Process for the production of solutions for use in the manufacture of colored artificial filaments and similar articles, which comprises reducing an acetone-insoluble indigo-type vat dyestufi, yielding an acetone-soluble leuco compound, in the presence of acetone so as to obtain a solution of the free leuco compound, removing insoluble material from such solution, oxidizing the leuco compound by kneading such acetone solution under oxidizing conditions with a plastic mass having a basis of a substance selected from the group consisting of cellulose formate, eellulose acetate, cellulose propionate, cellulose butyrate, methyl cellulose, ethyl cellulose and benzyl cellulose and then incorporating the kneaded mass in an acetone solution of said substance.

WILLIAM WHITEHEAD. 

